1. Field of Invention
The present invention relates to a control method and device of a backlight. More particularly, the present invention relates to a control method and device of a dynamic blinking backlight.
2. Description of Related Art
As some types of display panels cannot emit light themselves, they need to be disposed with backlights. For example, liquid crystal displays (LCDs) need backlights for the aid of displaying frames. With considerable improvement of the viewing angle and significant reduction in price, the trend of LCDs replacing cathode ray tube (CRT) displays as computer screens has already developed. And its next ambition focuses on a broader market, the household television. To achieve dynamic image quality display rivaling the CRT display, various well-known LCD manufacturers have started exploring the improvement of the dynamic features of LCDs. Quality degradation of LCDs when displaying dynamic images includes: reduction in dynamic contrast, edge-blur, and stroboscopic motion. The main reason lies in that the response speed of the liquid crystal is slow and the so-called Hold-type data writing feature.
To reduce the influence of the Hold-type data writing feature, the applicable methods can be divided into two categories: image temporary interruption and non-image interruption. The former imitates the CRT display to temporarily interrupt the image, not being received by the visual system; while the later increases the data renewal speed or compensates the dynamic track. Though the blinking backlight is a basic method for improving the dynamic image quality, it causes worries about extra power consumption and decrease in the service life of the lamp.
U.S. Pat. No. 4,958,915 discloses a liquid crystal apparatus, including a method of making the low-level brightness of the blinking backlight synchronous with the period of writing data to the display panel. This conventional technology makes the backlight blink at a fixed frequency, so as to imitate the CRT display to temporarily interrupt the image, thereby improving the dynamic features of LCDs. However, keeping the backlight blinking at a fixed frequency will cause extra power consumption and shorten the service life of the lamp.
U.S. patent application Ser. No. 20020154088 discloses a transmissive-type liquid crystal display apparatus. This conventional technology determines the on-and-off time of the cold cathode lamp based on the parameters of dynamic images, so as to turn off all the cold cathode lamps in the vertical blank period of a frame period, thereby improving the dynamic features of LCDs. Therefore, as the cold cathode lamp is kept blinking at a fixed frequency, this conventional technology will also cause extra power consumption and shorten the service life of the cold cathode lamp.
U.S. patent application Ser. No. 20040246242 discloses a display apparatus. This conventional technology determines the on-and-off time of the cold cathode lamp in a frame period based on the parameters of dynamic images. In other words, the ratio of lightening time to darkening time of the cold cathode lamp in a frame period is determined by the movement amount of the dynamic images, thereby improving the dynamic features of LCDs. Therefore, as the cold cathode lamp is kept blinking at a fixed frequency, this conventional technology will also cause extra power consumption and shorten the service life of the lamp.
U.S. patent application Ser. No. 20040051692 discloses a liquid crystal display device. This conventional technology controls the brightness of the backlight by adjusting the time proportion of the lightening and the darkening period in accordance with the brightness information in the display signal. This conventional cold cathode lamp is kept blinking at a fixed frequency without the capability of dynamically adjusting the blinking frequency in accordance with the features of the displayed image. As the cold cathode lamp is kept blinking at a fixed frequency, it will cause extra power consumption and shorten the service life of the lamp.